feat(hero): album-artist backdrop, configurable per-surface sources, and prefetch (#1193)

* refactor(cover): extract shared pickArtistBackdrop priority helper

* feat(hero): show the album artist's fanart as the mainstage hero backdrop

* feat(settings): configurable per-surface artist backdrop sources

Each artist-backdrop surface (mainstage hero, artist-detail header, fullscreen player) gets its own enable toggle + an ordered, individually-toggleable source list, configured under External Artwork Scraper on the Integrations tab (shown when the scraper is on). Reorder via the shared useDragSource/psy-drop drag infra plus keyboard-accessible up/down buttons; each source has its own on/off.

The shared chooser pickArtistBackdrop is generalised to resolveBackdrop + backdropFromConfig (ordered candidate list with the same pending/miss/centred-framing semantics), so all three surfaces resolve identically. themeStore persist bumped to v2; defaults reproduce today's order, so there is no visible change without user action.

Gating decoupled: the three surfaces are gated solely by their own per-surface flag, not by enableCoverArtBackground (which stays scoped to album/playlist-header cover blur). Reorder maths extracted to a pure, unit-tested module. i18n en + de (other locales TODO before PR).

Tests: resolver (10) + reorder (7).

* feat(cover): make the ensure queue surface-aware for artist backdrops

coverEnsureQueued now threads optional CoverEnsureOpts through to the Rust ensure and weaves the external surface into the in-flight key, so the fanart and banner surfaces of one artist no longer collide on one download chain. External surfaces also bypass the disk-src memory short-circuit (their {tier}-{surface}.webp never seeds those caches, and the canonical cover must not read as a hit). New thin ensureArtistBackdropQueued wrapper. Backward-compatible: plain covers append nothing to the key; the 5 queue tests stay green.

* fix(cover): reset the artist external-image hook synchronously on artist change

The hook reset src in an effect (one render late), so for the render between an artist change and that effect a consumer read the *previous* artist's resolved image. The mainstage hero then froze (and cached into per-album memory) a neighbouring slide's banner. Reset synchronously via the React adjust-state-on-prop-change pattern. Also removes brief stale-image flashes on the artist-detail header and fullscreen player.

* feat(hero): prefetch artist backdrops and show-ready-now / upgrade-on-re-entry

warmHomeMainstageCovers now prefetches each hero slide's artist backdrop (banner/fanart) at static slide-index priorities (idx1=high, idx0=low, rest=middle; no reprioritise on navigation), then predecodes every slide already on disk. useHeroBackdrop shows the best source ready at entry (Navidrome on a cold first visit, the prefetched/cached external one on re-entry) and freezes that source choice for the visit so nothing swaps mid-dwell; the url is derived live from the frozen choice, with a per-album disk memory for re-entry. HeroBg now crossfades only after the image bytes load (onLoad/complete gate + onError + fallback). Inert when the scraper is off. Tests: per-album memory (5).

* docs(changelog): configurable artist backdrops + mainstage hero (PR #1193)

CHANGELOG Added entry, settingsCredits line, and the What's New Artist-artwork highlight extended to cover the mainstage hero backdrop and per-place source config.

* docs(changelog): fold mainstage hero + per-place backdrops into the fanart entry (PR #1193)

Merge the configurable-backdrops changes into the existing 'Artist artwork from fanart.tv' block (now PR #1137 and #1193) instead of a separate entry.

* fix(hero): revert HeroBg load-gate that blanked the app (Maximum update depth)

The byte-load gate I added drove the crossfade reveal from an inline img ref + onLoad that re-fires on every render and scheduled a setTimeout each call; frequent re-renders (playback, marquee) stacked nested updates until React threw 'Maximum update depth exceeded' — and with no ErrorBoundary the whole window blanked. Reverted HeroBg to the proven timer-based crossfade. The hero only ever receives ready/predecoded urls, so the gate was cosmetic.

* fix(hero): gate the HeroBg crossfade on image load to stop the slide flicker

The bare 20 ms reveal faded a layer in before its bytes were ready (notably the Navidrome raw url), so a slide change flickered. Now an Image() preloader in the [url] effect reveals the layer on load (or a cached complete check), with a fallback. Everything is scheduled once per url — no per-render <img> ref/onLoad — so unlike the reverted gate it can't stack nested updates.

* feat(i18n): translate the backdrop-source settings into the remaining 10 locales

Adds the per-surface backdrop config strings (es, fr, nl, zh, nb, ru, ro, ja, hu, pl) and extends externalArtworkDesc to mention the mainstage hero where the key exists (ja has none → falls back to en).

src/components/settings/IntegrationsTab.tsx

@@ -6,6 +6,9 @@ import SettingsSubSection from '../SettingsSubSection';
 import { SettingsGroup } from './SettingsGroup';
 import { SettingsToggle } from './SettingsToggle';
 import { SettingsSubCard, SettingsField } from './SettingsSubCard';
+import { BackdropSourceList } from './BackdropSourceList';
+import type { BackdropSurface } from '../../store/themeStore';
+import type { BackdropSource } from '../../cover/artistBackdrop';
 import { MusicNetworkSection } from './musicNetwork/MusicNetworkSection';
 import { purgeExternalArtworkAllServers } from '../../api/coverCache';
 
@@ -14,6 +17,18 @@ export function IntegrationsTab() {
   const auth = useAuthStore();
   const theme = useThemeStore();
 
+  const backdropSurfaces: { key: BackdropSurface; label: string }[] = [
+    { key: 'mainstageHero', label: t('settings.backdropSurfaceMainstage') },
+    { key: 'artistDetailHero', label: t('settings.backdropSurfaceArtistDetail') },
+    { key: 'fullscreenPlayer', label: t('settings.backdropSurfaceFullscreen') },
+  ];
+  const backdropSourceLabel = (s: BackdropSource): string =>
+    s === 'banner'
+      ? t('settings.backdropSourceBanner')
+      : s === 'fanart'
+        ? t('settings.backdropSourceFanart')
+        : t('settings.backdropSourceNavidrome');
+
   return (
     <>
       <div
@@ -194,6 +209,34 @@ export function IntegrationsTab() {
               </SettingsSubCard>
             </SettingsGroup>
           )}
+          {theme.externalArtworkEnabled && (
+            <SettingsGroup
+              title={t('settings.backdropSourcesTitle')}
+              desc={t('settings.backdropSourcesSub')}
+            >
+              <SettingsSubCard>
+                {backdropSurfaces.map(({ key, label }) => (
+                  <div className="backdrop-surface-block" key={key}>
+                    <SettingsToggle
+                      label={label}
+                      checked={theme.backdrops[key].enabled}
+                      onChange={(v) => theme.setBackdropEnabled(key, v)}
+                    />
+                    {theme.backdrops[key].enabled && (
+                      <BackdropSourceList
+                        surface={key}
+                        sources={theme.backdrops[key].sources}
+                        labelFor={backdropSourceLabel}
+                        onChange={(next) => theme.setBackdropSources(key, next)}
+                        moveUpLabel={t('settings.backdropMoveUp')}
+                        moveDownLabel={t('settings.backdropMoveDown')}
+                      />
+                    )}
+                  </div>
+                ))}
+              </SettingsSubCard>
+            </SettingsGroup>
+          )}
         </div>
       </SettingsSubSection>